1. Field of the Invention
This invention relates generally to a soldering apparatus and, more specifically, to an apparatus for soldering an article, such as an electrical part-bearing printed wiring board, in an inert atmosphere.
2. Description of Prior Art
Because solder and metal portions to be soldered are susceptible to oxidation, it is desirable to perform a soldering operation in an inert gas atmosphere. JP-A-60-124464 discloses a soldering apparatus including a housing defining therein a soldering zone and having inlet and outlet openings positioned at positions lower than the soldering zone. An inert gas feeding port is provided in the top of the housing. The feeding port is connected to a source of the inert gas through a heater. Thus, the inert gas is heated in the heater and is fed to the top of the soldering zone. An article to be soldered is introduced through the inlet opening into the housing, conveyed upward to the soldering zone and, then, downward to the outlet opening. Since the soldering zone is positioned at a level higher than the inlet and outlet openings, the inert gas introduced into the soldering zone has a higher temperature (i.e. lower specific gravity) than the outside atmosphere, air is prevented from entering the soldering zone, so that the soldering operation can be performed in the inert gas atmosphere.
The known apparatus has, however, a drawback because it is necessary to provide a long vertical distance between the soldering zone and the inlet/outlet openings in order to prevent the outside air from entering the soldering zone. It is also necessary to slowly convey the article through the inside of the housing in order to suppress the creation of turbulent flows. Additionally, with the conventional apparatus, a large amount of the inert gas should be consumed to obtain satisfactory results.